This invention relates to a vehicular navigation system in which it is possible to search for an alternative suggested route when the vehicle is currently traveling on an already set suggested route.
A vehicular navigation system searches for a route from the present position of the vehicle to the destination and provides route guidance based upon the route found, thereby reducing the burden upon the driver when the vehicle is traveling on unfamiliar roads. To accomplish this, the vehicular navigation system has a function by which a route from the present position to the destination is retrieved in response to entry of the destination. The route found is displayed. The vehicular navigation system also has a function for detecting the present position of the vehicle and displays the present position along with the retrieved route to thereby provide route guidance.
In such a system which provides a unique route to the destination, a suggested route that is to the driver's liking is not always provided. More specifically, there are instances in which the driver does not wish to travel the initially retrieved route because the route would compel the driver to pass through a congested urban area. For example, in a vehicular travel guidance system disclosed in the specification of Japanese Patent Application Laid-Open No. 5-165407, a plurality of routes are found successively in accordance with a ranking that depends upon the cost of the line segment from the departure point to the destination set on a road map on the basis of digital map data. In order that other routes that differ from a previously found route may be found one after another, processing that raises the apparent cost of the line segment in the found route is executed, then a route for which the cost of the line segment is minimum is found, thereby making it possible to find and select a route that is an alternative to a route found earlier.
This vehicular travel guidance system is effective in a case where congested road conditions are already known at the time a route from the departure point to the destination is found. However, when an attempt is made to deal with a case in which the driver wishes to travel on another route owing to unexpected heavy traffic or road construction encountered during travel on a route, a destination must be set again using the present location as the starting point, a route to the destination must be found or another route must be found and selected in the manner mentioned above to bypass the congested section or the section under construction. Further, there are cases where an alternative route is searched for because a section of road is predicted to be congested as usual and cases where there is no congestion and the alternative route is the one having heavy traffic. In such cases a destination must still be set again in order to find another route, a route to the destination must be found or another route must be found and selected in the manner mentioned above to bypass the congested section or the section under construction.
Furthermore, another method that has been considered to deal with a case in which a section having heavy traffic or construction is encountered is to perform a search again upon deliberately departing from an initially set route, thereby bypassing the congested section of road or the road under construction. According to this function for performing a re-search, a route connecting to the already set suggested route from the present position of the vehicle is searched for when it is sensed that the vehicle has departed from the suggested route at such time that the vehicle is traveling along the already set suggested route. There are cases in which the congested section or the section under construction can be bypassed by using this function. However, in a case where the suggested route is deliberately departed from and the search is performed again, a route which connects to the already set suggested route is not always found and sometimes the route which the vehicle has entered is a dead end. In such case the search must be performed again upon driving the vehicle in a different direction from the route on which the vehicle is presently located. Further, even if the route can be connected to the route already set, the location of the connection may be in a section of heavy traffic or in a section under construction and therefore the route that is retrieved does not always make it possible to bypass such a section of road.
In the system which provides a unique route to the destination, a detour or roundabout road or a course desired to be traversed cannot be set in transit and it is difficult to make a course setting that is in line with the wishes of the driver.
Accordingly, a navigation system disclosed in the specification of Japanese Patent Application Laid-Open No. 2-3899 has an input unit for entering route information comprising a starting point, a destination and information indicating a transit location which the driver desires to traverse. Data in a recording unit that has recorded position data and road information entered from the input unit is processed in accordance with a navigation program and then outputted to a display unit. This makes it possible for the driver to designate the transit location desired to be traversed and to set the desired course. As a result, it is possible to provide route guidance in line with driver preference.
With a conventional navigation system of this kind, an en-route location desired to be traversed can be set but the route passing through this set location is still searched for and displayed. Accordingly, if the vehicle leaves the retrieved route before passing through the desired en-route location, the route to this location is not displayed; only the route to the final destination is displayed even if the driver wishes at all cost to pass through the location desired to be traversed.
Of course, if there is such an en-route location which the driver wishes to traverse at all cost, this location can be adopted as a provisional destination, the final destination can be entered after this location is reached and the search may then be performed. However, such an operation is troublesome for the driver to perform. In order to solve this problem, the applicant has proposed a vehicular navigation system in Japanese Patent Application Laid-Open No. 6-66587. This system is such that when an en-route location desired to be traversed has been set, guidance for a route that passes through this location is provided in reliable fashion. En-route location processing executed by this vehicular navigation system will be described below.
FIG. 1 is a diagram for describing the flow of processing for route guidance, and FIG. 2 is a diagram for describing processing for judging whether an en-route location has been traversed.
In route guidance, as illustrated in FIG. 1, first guidance is provided by a screen display or voice track in accordance with results of a search performed from the starting point to the en-route location (transit point) (step S401). The route to the en-route location is displayed on the screen by a red line, and the route from the en-route location to the destination is displayed in the form of a blue line. Next, it is determined whether the en-route location (transit point) has been traversed (step 402). If it is determined that the en-route location has been traversed, then en-route location traversal processing is executed (step S403) and the system changes over to route guidance for a route from the en-route location to the destination (step S404).
In the processing for determining whether the en-route location has been traversed, first it is determined whether the vehicle is traveling on the designated route (step S501), as shown in FIG. 2. If the vehicle is traveling on the route, it is determined whether the remaining distance to the en-route location on the route is less than a prescribed distance (200 m, for example) (step S502). If the distance is less than the prescribed distance (200 m), then it is decided that the en-route location has been passed. If the vehicle is not traveling on the route, on the other hand, it is determined whether the straight-line distance from the present position to the en-route location is less than a prescribed distance (200 m, for example) (step S503). If the straight-line distance is less than the prescribed distance (200 m), then it is decided that the en-route location has been passed.
In the system described above, however, the en-route location is either traversed with certainty or otherwise a decision regarding the en-route location will not be obtained unless a location within a distance corresponding to the en-route location is traversed. Consequently, if, when the driver wishes to set a desired route, an en-route location capable of being designated does not exist on this route, e.g., when the driver has set a station as the en-route location because the driver desires to take a road that passes in front of the station, as shown in FIG. 22A, it is judged that the en-route location has been traversed, and guidance to the destination can be received, so long as the road in front of the station resides in a range that is within the prescribed distance from the station. However, if the road in front of the station does not reside in the range within the prescribed distance, a decision to the effect that the en-route location has been passed is not obtained and guidance to the en-route location continues. In other words, in a case where a location just off a desired route can be designated as an en-route location in such a manner that the desired route can be selected, the driver does not actually intend to pass through the en-route location but the conventional system is such that the driver cannot receive guidance to the destination unless the en-route location is passed. Thus, with the conventional system described above, it cannot be arranged to receive route guidance conveniently by designating a so-called nearby dummy location as an en-route location.